As is also known in the art, an automotive sensor utilizing radio frequency (RF) signals to perform detection typically includes and RF antenna disposed within a sensor housing. Such a system is described in U.S. Pat. No. 6,501,415 assigned to the assignee of the present application.
As is also known, the sensor (and in particular the antenna within the sensor) typically interacts with its immediate environment. This interaction can cause disturbances of radiated fields which lead to degraded and unpredictable performance of the sensor.
To reduce, or ideally minimize, the interaction of the antenna within the sensor with its immediate environment, prior art techniques utilize either an RF absorptive foam or an RF shield disposed externally about the sensor. That is, prior art techniques typically utilize external absorptive materials (e.g. an RF absorptive plastic or other RF absorptive materials external to the sensor housing or outside the antenna box). Such an approach is illustrated in application number DE 102009042285 A1. Such an approach requires careful design of mounting/placement of the sensor behind fascia of a vehicle on which the sensor is mounted.
Furthermore, use of RF absorptive material (or more simply “absorber”) external to the sensor housing (and thus external to an antenna disposed in the sensor housing) usually requires a large amount of absorber to achieve the desired result. This, of course, adds size, weight and cost to the sensor. And while careful placement of external absorber can achieve the desired result, this is often difficult to control and is not always successful for every application.
Other approaches, such as that described in U.S. Pat. No. 6,496,138, describe various matching/lens techniques, to utilize a vehicle bumper as a radome for the sensor. Again, attaching absorber to the bumper (i.e. absorber external to the sensor) is suggested as part of this technique.
EP 1674882 describes a system which redirects and absorb reflections from a distant target to reduce multi-path target returns. This is accomplished by selecting a shape of a frame and applying absorber only on the surface of these shapes. As described in EP 1674882A1, this approach reduces reflections (multi-path) from close targets. The specially shaped frame is designed to direct reflected waves away from the antennas. An absorbing material can be disposed over the shaped frame to further reduce reflections and absorbing materials can be disposed on the radome to still further reduce reflections.